1. Field of the Invention
The present invention generally relates to a series-connected motor unit and a fan utilizing the series-connected motor unit and, more particularly, to a series-connected motor unit that provides a better vibration-proof effect by preventing the motor vibration from traveling between motors of the series-connected motor unit, and a fan utilizing the series-connected motor unit.
2. Description of the Related Art
Taiwanese Patent Number I322655 entitled “Circuit Board Holder, Dual Motor Apparatus and Dual Fan Structure” discloses a conventional series-connected motor unit as shown in FIG. 1. The series-connected motor unit includes two cooling fans 8 and a circuit board holder 9. Both the cooling fans 8 have a motor 81, a circuit board 82 and a plurality of vanes 83. The circuit board 82 can start operation of the motor 81 which, in turn, drives the vanes 83 to rotate. The circuit board holder 9 is disposed between the two cooling fans 8. The circuit board holder 9 consists of a plate 91 and a plurality of supporting members 92. The plate 91 has two faces 911 opposite to each other. The supporting members 92 are disposed on the plate 91 and protrude from the two faces 911. In this arrangement, the supporting members 92 are sandwiched between and abutted by the two circuit boards 82 when the two cooling fans 8 are assembled in series.
Since the circuit board holder 9 is disposed between the two cooling fans 8, a distance D is present between the two circuit boards 82. However, since the circuit board holder 9 abuts against the two circuit boards 82 only through the supporting members 92, the contact areas between the supporting members 92 and the two circuit boards 82 are very small. Thus, the supporting members 92 can only support and position the two circuit boards 82 in proper positions rather than prevent or relieve the motor vibration that travels between the two circuit boards 82. As a result, the motor vibration generated during operation of the two motors 81 will travel between the two motors 81. This not only affects the operation of the two cooling fans 8 but also shortens the service life of the two motors 81.
Furthermore, manufacturing of the circuit board holder 9 requires high sophistication. Specifically, the height H of the supporting members 92 protruding from the two faces 911 should be controlled in high accuracy in order to position the two circuit boards 82 in proper positions. Specifically, if the height H is too small, gaps may be present between the circuit board holder 9 and the two circuit boards 82, leading to loosening between the circuit board holder 9 and the two circuit boards 82. On the contrary, if the height H is too large, the circuit board holder 9 may over-press the two circuit boards 82, leading to damage of the two circuit boards 82.